1. Column 5 Amount of Securities Beneficially Owned Following Reported Transaction is held by Impresa Fund II LLC (157,382 Class A Common Stock), Impresa Fund III Limited Partnership (74,798 Class A Common Stock), Fidelity Biosciences Corp. (10,971 Class A Common Stock) and FIL Limited (1,224,933 Class A Common Stock). Column 5 does not include shares beneficially owned by Fidelity Management & Research Company as a result of acting as investment adviser to various investment companies as disclosed in Remark 1 below.

2. The price reported for this transaction is the weighted average price of multiple trades at prices ranging from $13.0000 to $13.0254. FMR LLC hereby undertakes to provide upon request by the Commission staff, the issuer, or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.

Remarks:

Remark 1: Fidelity Management & Research Company, a wholly owned subsidiary of FMR LLC and an investment adviser registered under the Investment Advisers Act of 1940, is the beneficial owner of Class A Common Stock of Ironwood Pharmaceuticals Inc. as a result of acting as investment adviser to various investment companies registered under the Investment Company Act of 1940. FMR LLC, Edward C. Johnson 3d and FIL Limited have no pecuniary interest in the Class A Common Stock beneficially owned by Fidelity Management & Research Company. Remark 2: FIL Limited directly holds 1,224,933 shares of Class A Common Stock of Ironwood Pharmaceuticals Inc. FMR LLC and FIL are of the view that they are not acting as a "group" for purposes of Section 13(d) under the Securities Exchange Act of 1934 (the "1934 Act") and that they are not otherwise required to attribute to each other the "beneficial ownership" of securities "beneficially owned" by the other corporation within the meaning of Rule 16a-1 promulgated under the 1934 Act. Therefore, they are of the view that the shares held by the other corporation need not be aggregated for purposes of Section 16(a). However, FMR LLC is making this filing on a voluntary basis as if all of the shares are beneficially owned by FMR LLC and FIL on a joint basis.

Scott C. Goebel, Duly authorized under Powers of Attorney effective as of June 1, 2008, by and on behalf of FMR LLC and its direct and indirect subsidiaries, by and on behalf of Edward C. Johnson 3d, and by and on behalf of FIL Limited

10/03/2012

** Signature of Reporting Person

Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person,
see
Instruction
4
(b)(v).